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1 | // (C) Copyright 2009-2011 Frederic Bron, Robert Stewart, Steven Watanabe & Roman Perepelitsa. |
2 | // | |
3 | // Use, modification and distribution are subject to the Boost Software License, | |
4 | // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
5 | // http://www.boost.org/LICENSE_1_0.txt). | |
6 | // | |
7 | // See http://www.boost.org/libs/type_traits for most recent version including documentation. | |
8 | ||
9 | #include <boost/config.hpp> | |
10 | #include <boost/type_traits/detail/yes_no_type.hpp> | |
11 | #include <boost/type_traits/integral_constant.hpp> | |
12 | #include <boost/type_traits/is_base_of.hpp> | |
13 | #include <boost/type_traits/is_const.hpp> | |
14 | #include <boost/type_traits/is_convertible.hpp> | |
15 | #include <boost/type_traits/is_fundamental.hpp> | |
16 | #include <boost/type_traits/is_integral.hpp> | |
17 | #include <boost/type_traits/is_pointer.hpp> | |
18 | #include <boost/type_traits/is_same.hpp> | |
19 | #include <boost/type_traits/is_void.hpp> | |
20 | #include <boost/type_traits/remove_cv.hpp> | |
21 | #include <boost/type_traits/remove_pointer.hpp> | |
22 | #include <boost/type_traits/remove_reference.hpp> | |
23 | ||
24 | // cannot include this header without getting warnings of the kind: | |
25 | // gcc: | |
26 | // warning: value computed is not used | |
27 | // warning: comparison between signed and unsigned integer expressions | |
28 | // msvc: | |
29 | // warning C4018: '<' : signed/unsigned mismatch | |
30 | // warning C4244: '+=' : conversion from 'double' to 'char', possible loss of data | |
31 | // warning C4547: '*' : operator before comma has no effect; expected operator with side-effect | |
32 | // warning C4800: 'int' : forcing value to bool 'true' or 'false' (performance warning) | |
33 | // warning C4804: '<' : unsafe use of type 'bool' in operation | |
34 | // warning C4805: '==' : unsafe mix of type 'bool' and type 'char' in operation | |
35 | // cannot find another implementation -> declared as system header to suppress these warnings. | |
36 | #if defined(__GNUC__) | |
37 | # pragma GCC system_header | |
38 | #elif defined(BOOST_MSVC) | |
39 | # pragma warning ( push ) | |
40 | # pragma warning ( disable : 4018 4244 4547 4800 4804 4805 4913) | |
41 | # if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000) | |
42 | # pragma warning ( disable : 6334) | |
43 | # endif | |
44 | #endif | |
45 | ||
46 | namespace boost { | |
47 | namespace detail { | |
48 | ||
49 | // This namespace ensures that argument-dependent name lookup does not mess things up. | |
50 | namespace BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl) { | |
51 | ||
52 | // 1. a function to have an instance of type T without requiring T to be default | |
53 | // constructible | |
54 | template <typename T> T &make(); | |
55 | ||
56 | ||
57 | // 2. we provide our operator definition for types that do not have one already | |
58 | ||
59 | // a type returned from operator BOOST_TT_TRAIT_OP when no such operator is | |
60 | // found in the type's own namespace (our own operator is used) so that we have | |
61 | // a means to know that our operator was used | |
62 | struct no_operator { }; | |
63 | ||
64 | // this class allows implicit conversions and makes the following operator | |
65 | // definition less-preferred than any other such operators that might be found | |
66 | // via argument-dependent name lookup | |
67 | struct any { template <class T> any(T const&); }; | |
68 | ||
69 | // when operator BOOST_TT_TRAIT_OP is not available, this one is used | |
70 | no_operator operator BOOST_TT_TRAIT_OP (const any&, const any&); | |
71 | ||
72 | ||
73 | // 3. checks if the operator returns void or not | |
74 | // conditions: Lhs!=void and Rhs!=void | |
75 | ||
76 | // we first redefine "operator," so that we have no compilation error if | |
77 | // operator BOOST_TT_TRAIT_OP returns void and we can use the return type of | |
78 | // (lhs BOOST_TT_TRAIT_OP rhs, returns_void_t()) to deduce if | |
79 | // operator BOOST_TT_TRAIT_OP returns void or not: | |
80 | // - operator BOOST_TT_TRAIT_OP returns void -> (lhs BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns returns_void_t | |
81 | // - operator BOOST_TT_TRAIT_OP returns !=void -> (lhs BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns int | |
82 | struct returns_void_t { }; | |
83 | template <typename T> int operator,(const T&, returns_void_t); | |
84 | template <typename T> int operator,(const volatile T&, returns_void_t); | |
85 | ||
86 | // this intermediate trait has member value of type bool: | |
87 | // - value==true -> operator BOOST_TT_TRAIT_OP returns void | |
88 | // - value==false -> operator BOOST_TT_TRAIT_OP does not return void | |
89 | template < typename Lhs, typename Rhs > | |
90 | struct operator_returns_void { | |
91 | // overloads of function returns_void make the difference | |
92 | // yes_type and no_type have different size by construction | |
93 | static ::boost::type_traits::yes_type returns_void(returns_void_t); | |
94 | static ::boost::type_traits::no_type returns_void(int); | |
95 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(::boost::type_traits::yes_type)==sizeof(returns_void((make<Lhs>() BOOST_TT_TRAIT_OP make<Rhs>(),returns_void_t()))))); | |
96 | }; | |
97 | ||
98 | ||
99 | // 4. checks if the return type is Ret or Ret==dont_care | |
100 | // conditions: Lhs!=void and Rhs!=void | |
101 | ||
102 | struct dont_care { }; | |
103 | ||
104 | template < typename Lhs, typename Rhs, typename Ret, bool Returns_void > | |
105 | struct operator_returns_Ret; | |
106 | ||
107 | template < typename Lhs, typename Rhs > | |
108 | struct operator_returns_Ret < Lhs, Rhs, dont_care, true > { | |
109 | BOOST_STATIC_CONSTANT(bool, value = true); | |
110 | }; | |
111 | ||
112 | template < typename Lhs, typename Rhs > | |
113 | struct operator_returns_Ret < Lhs, Rhs, dont_care, false > { | |
114 | BOOST_STATIC_CONSTANT(bool, value = true); | |
115 | }; | |
116 | ||
117 | template < typename Lhs, typename Rhs > | |
118 | struct operator_returns_Ret < Lhs, Rhs, void, true > { | |
119 | BOOST_STATIC_CONSTANT(bool, value = true); | |
120 | }; | |
121 | ||
122 | template < typename Lhs, typename Rhs > | |
123 | struct operator_returns_Ret < Lhs, Rhs, void, false > { | |
124 | BOOST_STATIC_CONSTANT(bool, value = false); | |
125 | }; | |
126 | ||
127 | template < typename Lhs, typename Rhs, typename Ret > | |
128 | struct operator_returns_Ret < Lhs, Rhs, Ret, true > { | |
129 | BOOST_STATIC_CONSTANT(bool, value = false); | |
130 | }; | |
131 | ||
132 | // otherwise checks if it is convertible to Ret using the sizeof trick | |
133 | // based on overload resolution | |
134 | // condition: Ret!=void and Ret!=dont_care and the operator does not return void | |
135 | template < typename Lhs, typename Rhs, typename Ret > | |
136 | struct operator_returns_Ret < Lhs, Rhs, Ret, false > { | |
137 | static ::boost::type_traits::yes_type is_convertible_to_Ret(Ret); // this version is preferred for types convertible to Ret | |
138 | static ::boost::type_traits::no_type is_convertible_to_Ret(...); // this version is used otherwise | |
139 | ||
140 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(is_convertible_to_Ret(make<Lhs>() BOOST_TT_TRAIT_OP make<Rhs>()))==sizeof(::boost::type_traits::yes_type))); | |
141 | }; | |
142 | ||
143 | ||
144 | // 5. checks for operator existence | |
145 | // condition: Lhs!=void and Rhs!=void | |
146 | ||
147 | // checks if our definition of operator BOOST_TT_TRAIT_OP is used or an other | |
148 | // existing one; | |
149 | // this is done with redefinition of "operator," that returns no_operator or has_operator | |
150 | struct has_operator { }; | |
151 | no_operator operator,(no_operator, has_operator); | |
152 | ||
153 | template < typename Lhs, typename Rhs > | |
154 | struct operator_exists { | |
155 | static ::boost::type_traits::yes_type s_check(has_operator); // this version is preferred when operator exists | |
156 | static ::boost::type_traits::no_type s_check(no_operator); // this version is used otherwise | |
157 | ||
158 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(s_check(((make<Lhs>() BOOST_TT_TRAIT_OP make<Rhs>()),make<has_operator>())))==sizeof(::boost::type_traits::yes_type))); | |
159 | }; | |
160 | ||
161 | ||
162 | // 6. main trait: to avoid any compilation error, this class behaves | |
163 | // differently when operator BOOST_TT_TRAIT_OP(Lhs, Rhs) is forbidden by the | |
164 | // standard. | |
165 | // Forbidden_if is a bool that is: | |
166 | // - true when the operator BOOST_TT_TRAIT_OP(Lhs, Rhs) is forbidden by the standard | |
167 | // (would yield compilation error if used) | |
168 | // - false otherwise | |
169 | template < typename Lhs, typename Rhs, typename Ret, bool Forbidden_if > | |
170 | struct trait_impl1; | |
171 | ||
172 | template < typename Lhs, typename Rhs, typename Ret > | |
173 | struct trait_impl1 < Lhs, Rhs, Ret, true > { | |
174 | BOOST_STATIC_CONSTANT(bool, value = false); | |
175 | }; | |
176 | ||
177 | template < typename Lhs, typename Rhs, typename Ret > | |
178 | struct trait_impl1 < Lhs, Rhs, Ret, false > { | |
179 | BOOST_STATIC_CONSTANT(bool, | |
180 | value = (operator_exists < Lhs, Rhs >::value && operator_returns_Ret < Lhs, Rhs, Ret, operator_returns_void < Lhs, Rhs >::value >::value)); | |
181 | }; | |
182 | ||
183 | // some specializations needs to be declared for the special void case | |
184 | template < typename Rhs, typename Ret > | |
185 | struct trait_impl1 < void, Rhs, Ret, false > { | |
186 | BOOST_STATIC_CONSTANT(bool, value = false); | |
187 | }; | |
188 | ||
189 | template < typename Lhs, typename Ret > | |
190 | struct trait_impl1 < Lhs, void, Ret, false > { | |
191 | BOOST_STATIC_CONSTANT(bool, value = false); | |
192 | }; | |
193 | ||
194 | template < typename Ret > | |
195 | struct trait_impl1 < void, void, Ret, false > { | |
196 | BOOST_STATIC_CONSTANT(bool, value = false); | |
197 | }; | |
198 | ||
199 | // defines some typedef for convenience | |
200 | template < typename Lhs, typename Rhs, typename Ret > | |
201 | struct trait_impl { | |
202 | typedef typename ::boost::remove_reference<Lhs>::type Lhs_noref; | |
203 | typedef typename ::boost::remove_reference<Rhs>::type Rhs_noref; | |
204 | typedef typename ::boost::remove_cv<Lhs_noref>::type Lhs_nocv; | |
205 | typedef typename ::boost::remove_cv<Rhs_noref>::type Rhs_nocv; | |
206 | typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Lhs_noref>::type >::type >::type Lhs_noptr; | |
207 | typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Rhs_noref>::type >::type >::type Rhs_noptr; | |
208 | BOOST_STATIC_CONSTANT(bool, value = (trait_impl1 < Lhs_noref, Rhs_noref, Ret, BOOST_TT_FORBIDDEN_IF >::value)); | |
209 | }; | |
210 | ||
211 | } // namespace impl | |
212 | } // namespace detail | |
213 | ||
214 | // this is the accessible definition of the trait to end user | |
215 | template <class Lhs, class Rhs=Lhs, class Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care> | |
216 | struct BOOST_TT_TRAIT_NAME : public integral_constant<bool, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _impl)::trait_impl < Lhs, Rhs, Ret >::value)>{}; | |
217 | ||
218 | } // namespace boost | |
219 | ||
220 | #if defined(BOOST_MSVC) | |
221 | # pragma warning ( pop ) | |
222 | #endif |